Processes are known for combining reinforcing fiber strands with thermoplastic resin to form reinforced plastic composites. U.S. Pat. No. 4,439,387 and Re. 32,772 sharing common inventorship herewith disclose the embedding of thermoplastic resin in reinforcing fiber strands as they are drawn through a forming die having a convoluted passage, in the presence of molten thermoplastic resin introduced from an extruder. The extrusion product of that process comprises an elongated bar or rod having a continuous length of reinforcing fiber encased within thermoplastic resin. That preformed composite may be inserted into a die of an injection molding machine, and utilized as an insert in a compound, composite product comprising an additional layer of thermoplastic resin molded over the insert. It is also known to cut the extrudate rod from the aforesaid forming die into short lengths for use as molding pellets. In the process of the aforesaid United States patents, the extruded rod comprising a fiber/resin composite is immediately cooled, prior to final forming and cutting to desired lengths.
U.S. Pat. No. 5,185,117, also having identity of inventorship herewith, discloses a process for compounding thermoplastic resin and fiber strands in an extruding compounder. According to the process of that patent, melted thermoplastic resin is introduced into the compounding extruder along with reinforcing fiber strands. The resulting extrudate consists of a molten mass of thermoplastic resin having discrete lengths of fiber strands randomly dispersed therein. This hot mixture may then be fed directly into a preform device to produce a measured preform for use in a compression molding machine. In the disclosed process of the '117 patent, the fiber strands are precut to desired lengths, before being introduced into the extruding compounder. The process and apparatus further requires a loss-in-weight scale to accurately measure predetermined quantities by weight of reinforcing fiber strands to be controllably introduced into the compounding extruder in the presence of thermoplastic resin. A separate loss-in-weight feed scale assembly is required to accurately convey predetermined amounts by weight of the thermoplastic resin into the compounding extruder for mixing in the desired proportions with the reinforcing fiber strands. The loss-in-weight scales necessarily add to the cost and complexity of the compounding apparatus.
U.S. Pat. No. 4,616,989 discloses an apparatus for incorporating glass fiber strands into thermoplastic resins in which a premixing chamber is utilized to initially mix glass fiber strands with molten resin. This mixture is then fed into a two-stage screw-type extruder to complete the mixing of the fiber strands and resin. The resin-fiber mass as discharged from the final extruder is passed through a forming die having a plurality of orifices. This serves to form the material into elongated filaments of glass fiber reinforced resin which are then cooled, and then granulated for use as a molding compound.
U.S. Pat. No. 2,877,501 to Brandt discloses a process for forming granules comprised of glass fiber strands coated with a molding plastic, which are intended for use as feed stock for an injection molding machine. In the Brandt process, fiber strands are pulled through an orifice within which they are coated with a resin material.
None of the known prior art processes for formulating a mixture of fiber reinforced resin for molding purposes are operatively effective for preparing a molding material comprised of fiber reinforced resin for immediate introduction into a molding machine at the same site where the fiber-resin mixture is made. Nor can any of the known prior art processes for formulating a mixture of fiber reinforced resin for molding purposes operate in a controlled and accurate discontinuous manner. Either cumbersome and costly apparatus, including multiple stage mixing devices and loss-in-weight scales, are required in the prior processes, and/or the fiber-reinforced resin is extruded into lengths, cut and packaged for sale and transportation to separate molding facilities.
There thus exists a need for a compact, efficient apparatus and process for accurately formulating mixtures of fiber and resin and thereafter directly introducing that molding material directly into a molding machine, such as an injection molding machine, a compression molding press, a transfer mold, a blow mold, a profile extrusion machine or an inject compression molding machine. In addition, there also exists a need for an apparatus and process capable of operating in a discontinuous manner to allow the admixture of variously sized batches of fiber reinforced resin molding material.